The present invention relates to a toner for electrophotography for forming images in electrophotography, electrostatic recording and the like and a process for production thereof.
In recent years, in accordance with the requirements for enhanced definition of electrostatic images obtained by copiers and printers utilizing electrophotographic systems, attempts have been made to use a toner having smaller particle size as a developer.
When a toner is reduced in particle size, however, such problems will arise that frictional electrification increases due to an increase in specific surface area to degrade image quality or that adhesion between toner particles will increase to cause toner components to be fixed onto photoreceptors. In order to solve such problems, it is proposed that strontium titanate be used as an external additive for toners (refer to Patent References 1 and 2, for example).
Being almost neutral in electrostatic propensity and high in dielectric constant, strontium titanate is characterized in that it has an invariable electrification level. Also, strontium titanate is disposed to act as an abrasive to scrape off any fixed stuff on photoreceptors.
Using strontium titanate in large quantities will however cause a decrease in flowability, resulting in toner aggregation due to stress or the like within developing machines during continual copying. As such, a problem, so-called “aggregation noise” will arise in which cores of aggregates and decreases in image density (white spots) around the cores are created in solid images.
Also, depending on the kind of strontium titanate, fogging due to toner scattering and scratches on photoreceptors have sometimes been caused.    Patent Reference 1: Japanese Unexamined Patent Publication Hei 10-010770    Patent Reference 2: Japanese Unexamined Patent Publication No. 2003-277054